What are chemical messengers that control growth, differentiation, and the metabolism of specific target cells called?

Neurons are specialized cells that transmit electrical signals throughout the nervous system. While they play a vital role in communication within the body, they do not function as chemical messengers in the manner that hormones do. Instead, neurons communicate through neurotransmitters at synapses, which is different from the hormonal signaling pathway.

Glands are organs that produce and secrete hormones, but they themselves are not the chemical messengers. Instead, they are responsible for synthesizing and releasing hormones into the bloodstream, where these hormones then act on target cells to elicit physiological responses.

Second messengers are molecules that relay signals received at receptors on the cell surface to target molecules inside the cell. They play a key role in the signaling pathways initiated by hormones but are not chemical messengers themselves. Instead, they act as intermediaries that amplify and propagate the hormonal signal within the cell.